The present invention relates to power-on reset circuit which is utilized for an IC card that obtains electric power from the external electric power supply source without contacting, for example, through electromagnetic waves.
In recent years, an IC card with a semiconductor integrated circuit device is becoming widespread. The IC card has a capability of exchanging information between an external reader/writer apparatus and a semiconductor integrated circuit device mounted in the IC card. This makes it possible to store necessary information in an internal nonvolatile memory of the semiconductor integrated circuit device, and conversely, to read information from the nonvolatile memory. By utilizing such an IC card, it is possible to realize a variety of functions that a magnetic card has carried out conventionally.
With a resent advance in the technology for large packing densities, the IC card has included a nonvolatile memory with a larger capacity. Accordingly, a multi-purpose card having a plurality of applications included in one IC card is also becoming widespread.
Further, non-contact type IC card system for the IC card has been studied in which the supply of electric power without contacting as well as data communication are carried out, utilizing electromagnetic waves with carrier frequencies of the order of several MHz to several tens of MHz. In case of non-contact type communication by using the IC card, no terminals for contacting is necessary, and no damages are caused in a contacting part of such terminals. Therefore, the IC card has advantages such as decrease in maintenance cost and easy handling.
One of the significant features of the non-contact type IC card system is that it is possible to arrange a system capable of a speedy and easily operable information exchange processing. For example, non-contact type IC card serving as a ticket for taking transport facilities such as a train and a bus allows a person to go through the ticket gate only by ways of holding the non-contact type IC card over the ticket gate (hereinafter referred to as xe2x80x9cholding processxe2x80x9d), or making the non-contact type IC card touch to the ticket gate in a moment (hereinafter referred to as xe2x80x9ctouch-and-go processxe2x80x9d).
Thus, in such a non-contact type IC card system, considered are various manners for information exchange between an IC card and a reader/writer apparatus. Some examples are given as follows: (1) a way of holding the IC card over the reader/writer apparatus at a small distance within approximately several cm (holding process); (2) a way of inserting the IC card to a card holder set in the reader/writer apparatus (inserting process); and (3) a way of supplying voltage to the IC card at power-on in setting the IC card to the reader/writer apparatus.
These ways are different from each other in how to make the IC card close to the reader/writer apparatus. Accordingly, they are different from each other in a condition inside the IC card for producing a power supply voltage when supplying power by electromagnetic induction from the reader/writer apparatus to the IC card.
Further, electromagnetic induction makes it impossible to supply a large amount of electric power and causes variations in the amount of the power supply. Therefore, a power-on reset operation in starting the supply of power must be highly reliable.
The following will explain what kind of power-on reset or malfunction preventing circuit of a reset circuit is used in a conventional non-contact type IC card.
For example, Japanese Laid-Open Patent Publication No. 269327/1998 (Tokukaihei 10-269327) discloses a circuit configuration for carrying out the power-on reset with respect to the non-contact type IC card. In the technology described in the publication, the power of the logic circuit is shut off on the reset operation by detection of power supply voltage in an analog mode. This shut-off does not apply voltage to an input/output circuit to/from a microcomputer and a microcomputer circuit. The configuration will be described more specifically below.
FIG. 10 is a circuit diagram of an example of the circuit configuration. Voltage outputted from an antenna coil 51 is supplied to each circuits after supplied to REG-A 55 and REG-B 56 as regulator circuits, and VREF 57 as a reference voltage producing circuit. From the REG-A 55, voltage is supplied to a microcomputer 64 and an interface section thereof. Further, from the REG-B 56, voltage is supplied to a CLK reproducing circuit 53, a reset producing circuit 54, an MOD 66 as a modulation circuit, a DEMO 67 as a demodulation circuit, and (+) terminal of a comparator circuit 59.
The output from the VREF 57 as a reference voltage producing circuit is for the voltage supply to the REG-A 55 and the REG-B 56, and a switch 60 is provided on the path to the REG-A 55 to control a power rising sequence. Further, the output from the VREF 57 is connected to a (+) terminal of a comparator circuit 58 for controlling ON/OFF operation of the switch 60.
The output voltages of the REG-A 55 and the REG-B 56 may be at the same potential or at a different potential. However, it is preferable that the REG-A 55 and the REG-B 56 have the same circuit configuration as a regulator.
Here, as a result of comparison in power rising rate among an analog detecting section including a resistor 61 and a diode 62, the VREF 57, the REG-A 55, and the REG-B 56, the REG-A 55 and the REG-B 56 rises in a most slow rate among them. The analog detecting section rises in a fastest rate, and the VREF 57 rises in a secondly fastest rate. By taking advantage of the difference in power rising rate, the power rising is controlled as follows.
First, the comparator circuit 59 determines which output voltages of the REG-B 56 and the VREF 57 is larger. In usual operation, the output voltage of the REG-B 56 is larger than that of the VREF 57. However, the power rising rate of the REG-B 56 is relatively slow as described above. Therefore, at the moment when the non-contact type IC card is held over the reader/writer apparatus, the output voltage of the VREF 57 becomes larger than that of the REG-B 56.
In such a situation, since the magnitude of the power supply voltage supplied to the microcomputer 64 is not sufficient for its stable operation, the microcomputer 64 must be in a reset state. Therefore, the reset producing circuit 54 produces a reset signal in accordance with the result of the comparison in the comparator circuit 59. The reset signal is provided to the microcomputer 64 via a buffer circuit 69 D. Thus, the microcomputer 64 can operate, being released from a reset state, only when power supply voltage sufficient for a stable operation is supplied thereto.
However, the microcomputer 64 cannot always obtain intended signals from the outputs of buffer circuits 69A to 69 D in unstable operations by the logic circuits such as the reset producing circuit 54. In other words, a reset releasing signal may be outputted to the microcomputer 64 in a low power supply voltage before the output of the REG-A 55 is provided to the microcomputer 64 In such a case, the voltage of other terminals becomes higher than that of the microcomputer 64, which results in damage and malfunction of elements in the microcomputer 64. Also, the same event may occur in a terminal for clock and a terminal for data.
To prevent such disadvantages, it is arranged in the configuration shown in FIG. 10 that the switch 60 is provided on the path over which reference voltage supplied to the REG-A 55 flows, and the switch 60 disconnects so as not to supply power to the microcomputer 64 during the period that an adequately large voltage for operation cannot be available. Further, the same power source as the microcomputer 64 is connected to the buffer circuits 69A to 69D so that the voltage larger than that of a power source terminal cannot be applied to other terminals of the microcomputer 64.
Still further, the switch 60 carries out switching operation in accordance with a logic produced by an AND circuit 63 so that malfunction may not occur during the period that logic circuits such as the reset producing circuit 54 keeps unstable operation. The AND circuit 63 outputs each AND of the outputs of the reset producing circuit 54, the comparator circuit 59, and the comparator circuit 58. Such an AND circuit 63 can be realized by a simple transistor logic, so that the AND circuit 63 ensures a stable operation even in a low power source voltage.
The comparator circuit 58 compares between the output of the VREF 57 and a forward voltage of the diode 62. Usually, a rising of a forward voltage, which is obtained from bias current, of the diode 62 is fast. Therefore, the comparator circuit 58 outputs a logic xe2x80x9cLxe2x80x9d to the AND circuit 63 until the output of the VREF 57 makes a rising. Consequently, the output from the AND circuit 63 allows the switch 60 to be connected to a GND side so that the REG-A55 cannot make a false rising.
Further, the comparator circuit 59 compares between the outputs of the REG-B 56 and the VREF 57. Usually, the rising of the VREF 57 is faster than that of the REG-B 56. Therefore, the comparator circuit 59 outputs a logic xe2x80x9cLxe2x80x9d to the AND circuit 63 until the output of the REG-B 56 makes a rising. Consequently, the output from the AND circuit 63 allows the switch 60 to be surely connected to a GND side until the output of REG-B 56 makes a rising.
Further, during the period that the reset signal is not a logic xe2x80x9cHxe2x80x9d sufficiently, the output of the reset producing circuit 54 is inputted to the AND circuit 63 in such a manner that the switch 60 is connected to the GND side.
As described above, after the analog detecting section which includes the register 61 and the diode 62 ensures succession of its operation to the VREF 57, the REG-A 55, and the REG-B 56, a reset release is carried out, so that no false operation occurs.
Meanwhile, in recent years, with an increasing demand for the non-contact type IC card system, a considered form for usage is the conventional contact type IC card including capabilities of the non-contact type IC card, and it is distinguished between the use of the non-contact type IC card and the use of the contact type IC card according to purposes. Accordingly, a combination card that capabilities of non-contact type and contact type IC cards are integrated in one card can correspond to both systems of the non-contact type IC card system and the contact type IC card system, so that it is expected that the combination card will be popular in future.
Note that, the non-contact type IC card system has some types such as an adjacent type and a vicinity type according to its communication distance. Standardization of these types are promoted currently in ISO/IEC14443 and ISO/IEC10536.
As described above, there are various forms of the non-contact type IC card for usage, and a rising waveform of the voltage supplied from a non-contact type reader/writer apparatus varies depending on each situation in using such an IC card. This makes it difficult to detect voltages in the semiconductor integrated circuit device mounted in the IC card. That is, a condition setting of power-on-reset is highly difficult in a technical aspect, thereby making a design of the non-contact type reader/writer apparatus difficult.
Here, referring to FIGS. 11 and 12, the following will describe the rising waveform of the voltage supplied from the reader/writer apparatus and a reset period to be expected. In these drawings, a REGIN voltage is a voltage rectified by a bridge diode. In an example of the arrangement shown in FIG. 10, the REGIN voltage corresponds to the output from a diode bridge 52 to elements such as an REG-A 55. Further, a VCC2V voltage is a logic power supply of two volt produced from the REGIN voltage via a regulator. In the example of the arrangement shown in FIG. 10, the VCC2V voltage corresponds to the output voltage of REG-A 55
FIG. 11 shows a rising waveform of voltage by a switching operation of the reader/writer apparatus. The rising waveform of the REGIN voltage is sharp at this moment, and a rising period of the REGIN voltage is influenced by rectifying action of an antenna coil (an antenna coil 51 in FIG. 10), a diode bridge (a diode bridge 52 in FIG. 10), and a smoothing capacitor (a smoothing capacitor 68 in FIG. 10). In the present switching operation, the rising period of the REGIN voltage is set as a tREGIN period.
At this point, a rising period of a regulator that produces a logic voltage VCC2V is nearly equal to the rising period of the REGIN voltage. The VCC2V voltage rises with a little delay after the rising of the REGIN voltage, and its rising waveform is sharp. According to an actual measurement, the tREGIN period is in the order of several tens of xcexcsec. In such a case of the rising waveform, a reset signal can be released after a required period for system initialization, setting a rising point of VCC2V voltage as an initial point.
FIG. 12 shows a rising waveform of voltage in the operations described previously, that is, in a holding operation, a inserting operation, or a touch-and-go operation. At this moment, the rising waveform of the REGIN voltage is gradual. According to the actual measurement, the tREGIN period, a rising period of the REGIN voltage, is in the order of several hundreds of msec. In such a case, the VCC2V voltage starts rising when the REGIN voltage reaches a set voltage level, although it depends on settings of the regulator. That is, in case where the rising waveform of the REGIN voltage is gradual, the VCC2V voltage reaches a target voltage before the REGIN voltage makes a complete rising.
In such a case of the rising waveform, the reset signal can be released at a rising point of the VCC2V voltage as an initial point. However, it is necessary to release the reset signal after the rising of the REGIN voltage as a main power supply, and an extremely long reset period is required as compared with the case shown in FIG. 11.
In the circuit shown in FIG. 10 as described previously, in case where the rising of the voltage is thus gradual, gate output of the AND 63 is unstable in the course of a transitional rising of the output from the REG-B 56 corresponding to the VCC2V voltage. This causes the malfunction of the switch 60, and as a result, there is a possibility that a reset release cannot be normally carried out.
Thus, a reset period varies between the case of a sharply rising voltage and the case of a gradually rising voltage, there is a problem that it is difficult to produce reset periods in the same reset circuit.
Further, in the IC card used in the conventional non-contact type IC card system, the available amount of a current by an LSI is not more than 10 mW. However, in a recent multi-purpose IC card, with the increasing number of applications stored in a nonvolatile memory, demand for an IC card with a large capacity is increasing. This increases the amount of a current required for the LSI to the order of about 200 mW. This arises a big problem in the non-contact type IC card system having a limited capability of power supply as described previously. Accordingly, a possibility rises that the lowering of power supply voltage is caused especially in writing/erasing to the non-volatile memory that consumes a large electric power. That is, the non-contact type IC card system has a problem that this change in the power supply voltage is falsely recognized as a rising of the power supply voltage. Therefore, it is necessary to give some contrivance to the reset circuit.
Further, the use of an A/D converter or a sophisticated analog detecting circuit for detection of power supply voltage must be avoided to prevent an additional increase in the amount of current consumed in the reset circuit. The use of such an arrangement results in not only the increase in the amount of a consumed current, but also the increase in the size of a circuit.
An object of the present invention is to provide a power-on reset circuit which outputs a reliable and effective reset signal even in case where the rising of electric power obtained from an external power supply source varies.
To achieve the above object, a power-on reset circuit according to the present invention, provided in a system in which a power voltage is obtained from an external power supply source without contacting by electromagnetic induction, a power voltage thus obtained is converted into a predetermined voltage and supplied to a logic section which performs a logic operation, produces a reset signal for controlling a reset state of the system. The power-on reset circuit includes:
a first reset circuit for detecting a voltage supplied to the logic section so as to produce a first reset signal;
a second reset circuit for detecting an output voltage of a rectifying circuit which rectifies a power voltage thus obtained from the external power supply source so as to produce a second reset signal; and
a reset signal outputting circuit for outputting as the reset signal either the first reset signal or the second reset signal.
In case where electric power is obtained from the external power supply source without contacting by electromagnetic induction, conditions for production of the power voltage varies depending on situations, for example, in cases of a sharply rising power voltage and a gradually rising power voltage.
In case where power voltage rises sharply, the output voltage of the rectifying circuit also rises sharply, and thereafter, the voltage supplied to the logic section rises sharply. In such a case, if it is checked that the voltage supplied to the logic section has rose, this means that the output voltage of the rectifying circuit also rises. Therefore, the reset signal outputting circuit can output as a reset signal the first reset signal from the first reset circuit which detects the voltage supplied to the logic section.
On the other hand, in case where power voltage rises gradually, the output voltage of the rectifying circuit and the voltage supplied to the logic section also rises gradually. Here, the completely rising output voltage of the rectifying circuit is higher than the completely rising voltage supplied to the logic section, so that the rising of the voltage supplied to the logic section is completed more quickly in case where the power voltage rises gradually. Therefore, the reset signal outputting circuit can output as a reset signal the second reset signal from the second reset circuit which detects the output voltage of the rectifying circuit.
Thus, according to the above arrangement, it is possible to provide the power-on reset circuit which can surely control the reset state of the system in either case of a sharply rising power voltage and a gradually rising power voltage.
Further, the IC apparatus according to the present invention includes the above power-on reset circuit.
Application of the above power-on reset circuit to, for example, an IC apparatus like as an IC card can surely control the reset operation with respect to various functional blocks inside the IC apparatus, for example, even in a non-contact type IC apparatus making unstable power supply from the external power supply source. Therefore, it is possible to realize that IC apparatus which secures the stable operation.
Further, it is also possible to realize the IC card used as both non-contact type card and contact type card by providing contact type terminals to the above non-contact type IC card.
For a fuller understanding of the nature and advantages of the invention, reference should be made to the ensuing detailed description taken in conjunction with the accompanying drawings.